In general, a gas turbine includes a compressor, a combustor, and a turbine. A turbine, which is a power generating device that converts heat energy of fluids (e.g., gas, steam, etc.) into mechanical energy such as rotational force, for example, includes a rotor with a plurality of buckets so as to be axially rotated by the fluid, and a casing with one or more diaphragms installed to surround the rotor. As the compressor rotates, outside air is sucked in and compressed to be sent to the combustor. The compressed air and fuel is mixed with each other in the combustor such that combustion occurs. High-pressure and high-temperature gas generated in the combustor rotates the rotor of the turbine as the high-pressure and high-temperature gas flow through the turbine. The rotation of the rotor may drive a generator, for example, to generate electricity.
In a steam turbine, a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine are connected in series or in parallel to rotate the rotor. In a case of serial connection, the high-pressure turbine, the medium-pressure turbine, and the low-pressure turbine share one rotor. Each of the turbines includes diaphragms and buckets based on the rotor in the casing, and steam rotates the rotor while passing through the diaphragms and the buckets, thereby driving a generator, for example.
In this case, the gas turbine and the steam turbine have a structure in which a rotating body (rotor) rotates with respect to a fixed body (diaphragm). Therefore, high-temperature and high-pressure fluid may leak due to a gap between the fixed body and the rotating body, thereby causing decrease in energy efficiency due to power loss. There has been continual efforts to decrease the leakage of fluid through the gap between the rotating body and the fixed body.
In order to minimize the leakage of fluid, the gap between the rotating body and the fixed body needs to be minimized. However, there are various restrictions in narrowing the gap. For example, if the gap is excessively narrow, interference between the rotating body and the fixed body can occur upon axial rotation of the rotating body, such that vibration is generated due to rubbing, which causes severe damage to the turbine.
Meanwhile, in the steam turbine, since the high-temperature steam introduced from a boiler heats the rotating body and the fixed body, the rotating body and the fixed body may expand or contract by several millimeters to several tens of millimeters depending on the position at the time of the operation and the start and stop. Here, since material characteristics of the rotating body and the fixed body are different from each other, the rotating body and the fixed body expand or contract differentially. Further, an expanding direction is also different depending on the turbine structure. Therefore, the interference is caused between the rotating body and the fixed body during the operation, thereby causing rubbing.
Recently, sealing technology including a honeycomb seal and a labyrinth seal to reduce the gap between a rotating body and a fixed body have been used in gas and steam turbines in which the honeycomb seal and the labyrinth seal flexibly contact each other.
Referring to FIG. 1, a honeycomb seal 3 is disposed on the fixed body 4 of the turbine, and labyrinth seal 2 is disposed on the rotating body 1 of the turbine so as to adjacently face the honeycomb seal 3. In this case, a gap between the honeycomb seal 3 and the labyrinth seal 2 is narrowed, and the number of tooth of the labyrinth seal 2 is increased in order to prevent leakage of fluid as shown by arrows illustrated in FIG. 1.
When the gap is narrowed so that the honeycomb seal 3 and the labyrinth seal 2 do not contact each other, a space through which the fluid may leak is reduced. When the number of tooth of the labyrinth seal 2 is increased, fluid pressure is decreased every time the fluid passes through the tooth, thereby slowing down the flow of leaked fluid. As such, the leakage of the fluid through the gap between the rotating body 1 and the fixed body 4 of the turbine is prevented or minimized.
However, according to the existing sealing method and structure, even though a predetermined gap is formed between the honeycomb seal 3 and the labyrinth seal 2, the gap may change due to vibration and thermal expansion of the materials, etc. during the operation of the turbine, thereby increasing the wear rate of the sealing components due to rubbing. This ultimately may lead to damage to blade or turbine components. Further, as the sealing components wear down, sealing capability is degraded, and the fluid is leaked, such that output efficiency of the turbine is deteriorated.
Therefore, an apparatus capable of maintaining the sealing capability even when the sealing gap between the rotating body 1 and the fixed body 4 is moderately widened depending on the operational environment of the turbine is required.